http://java-websocket.org/ "A barebones WebSocket client and server implementation written in 100% Java"
http://grizzly.java.net/ Framework for building web servers of various scales and types incl Web Socket client & server apis.
Java Web Container http://tomcat.apache.org/download-70.cgi new api & sup[port in 7.0.7: http://tomcat.apache.org/tomcat-7.0-doc/api/index.html?org/apache/catalina/websocket/package-summary.html
http://glassfish.java.net/ WebSockets via Grizzly and latterly WebSocket SDK also.
http://autobahn.ws/developers Including Android web socket client
http://code.google.com/p/weberknecht/ Project with Java SE / Android clients
http://www.eclipse.org/jetty/ Java Web Container including WebSockets support, client and server apis.
Java Server including web container with WebSockets support. see for example: http://www.caucho.com/resin-4.0/examples/websocket-java/index.xtp
Gateway products, includes Java developer APIs for web sockets. e.g. http://tech.kaazing.com/documentation/dragonfire/howto-java.html
Prototyping high level APIs & annotations for Web Sockets. http://java.net/projects/websocket-sdk
Proposing API for server side of Http Upgrade mechanism to enable websockets support to be build on the Servlet Container e.g.: http://java.net/projects/servlet-spec/lists/jsr340-experts/archive/2012-02/message/8
"The only Portable WebSocket/Comet Framework supporting Scala, Groovy and Java" https://github.com/Atmosphere/atmosphere
"Websockets4j Is a simple implementation of the WebSockets protocol. Currently supports the plain text version of Drafts 75 and 76 of the protocol." http://code.google.com/p/websockets4j/
"GNU WebSocket4J is a WebSocket protocol implementation in Java. It allows you to build Web applications that interact with applications running in a JVM. GNU WebSocket4J implements both server and client side of the protocol, so it can be used to build both WebSocket servers and clients." http://maarons.alwaysdata.net/software/GNU/WebSocket4J/
Starting to work on it. I'm not sure how it is related to Tomcat's support for WebSockets.)
Asynchronous event-driven network application framework, including websockets amongst many other things.
TorqueBox Ruby application server built on JBoss AS7 and JRuby. http://torquebox.org/documentation/http://torquebox.org/news/2011/08/15/websockets-stomp-and-torquebox/